mess around (with sb) phrase mainly US informal
If a married man or woman messes around with someone, they have a sexual relationship with someone who is not their wife or husband.
She found out that her husband was messing around with his secretary. 她发现丈夫和他的秘书偷情。
pick sb up phrase informal
to start a sexual or romantic relationship with someone you do not know, by talking to that person and giving them a lot of attention:
He said he'd picked the woman up in a bar. 他说他在酒吧勾搭上了那个女人。

(Translation of 勾搭 from the Cambridge Chinese (Simplified)-English Dictionary © Cambridge University Press)